Method for recording data in optical recording medium, an apparatus for recording data in optical recording medium and optical recording medium

ABSTRACT

It is an object of the present invention to provide a method for recording data in an optical recording medium which can record data in a write-once type optical recording medium at a high linear recording velocity using a laser beam having a low recording power. The method for recording data in an optical recording medium according to the present invention is constituted so that when data are to be recorded in an optical recording medium including a substrate, a first recording layer and a second recording layer by projecting a laser beam whose power is modulated in accordance with a pulse train pattern including pulses whose levels are set to levels corresponding to a recording power Pw and a bottom power Pb onto the optical recording medium and forming a recording mark at a predetermined region of the first recording layer and the second recording layer, as a linear recording velocity increases, the power of the laser beam is modulated using a pulse train pattern including a smaller number of pulses whose level is set to a level to the recording power Pw, thereby forming a recording mark. According to the present invention, since the power of a laser beam is modulated using a pulse train pattern including a smaller number of pulses whose level is set to a level to the recording power Pw as a linear recording velocity increases, it is possible to record data in an optical recording medium using a laser beam having a low recording power even when a linear recording velocity is high and on the other hand, it is possible to prevent cross-talk of data from increasing even when a linear recording velocity is low. Therefore, it is possible to employ a semiconductor laser having a relatively low output even when data are recorded at a high linear recording velocity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for recording data in anoptical recording medium, an apparatus for recording data in an opticalrecording medium and an optical recording medium, and particularly, to amethod for recording data in an optical recording medium and anapparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium using a laserbeam having a low recording power at a high linear recording velocityand a write-once type optical recording medium in which data can berecorded using a laser beam having a low recording power at a highlinear recording velocity.

2. Description of the Related Art

Optical recording media such as the CD, DVD and the like have beenwidely used as recording media for recording digital data. These opticalrecording media can be roughly classified into optical recording mediasuch as the CD-ROM and the DVD-ROM that do not enable writing andrewriting of data (ROM type optical recording media), optical recordingmedia such as the CD-R and DVD-R that enable writing but not rewritingof data (write-once type optical recording media), and optical recordingmedia such as the CD-RW and DVD-RW that enable rewriting of data (datarewritable type optical recording media).

As well known in the art, data are generally recorded in a ROM typeoptical recording medium using pre-pits formed in a substrate in themanufacturing process thereof, while in a data rewritable type opticalrecording medium a phase change material is generally used as thematerial of the recording layer and data are recorded utilizing changesin an optical characteristic caused by phase change of the phase changematerial.

On the other hand, in a write-once type optical recording medium, anorganic dye such as a cyanine dye, phthalocyanine dye or azo dye isgenerally used as the material of the recording layer and data arerecorded utilizing changes in an optical characteristic caused bychemical change of the organic dye, or chemical change and physicalchange of the organic dye.

Further, there is known a write-once type recording medium formed bylaminating two recording layers (See Japanese Patent Application LaidOpen No. 62-204442, for example) and in this optical recording medium,data are recorded therein by projecting a laser beam thereon and mixingelements contained in the two recording layers to form a region whoseoptical characteristic differs from those of regions therearound.

In this specification, in the case where an optical recording mediumincludes a recording layer containing an organic dye, a region in whichan organic dye chemically changes or chemically and physically changesupon being irradiated with a laser beam is referred to as “a recordingmark” and in the case where an optical recording medium includes tworecording layers each containing an inorganic element as a primarycomponent, a region in which the inorganic elements contained in the tworecording layers as a primary component are mixed upon being irradiatedwith a laser beam is referred to as “a recording mark”.

An optimum method for modulating the power of a laser beam projectedonto an optical recording medium for recording data therein is generallycalled “a pulse train pattern” or “recording strategy”.

FIG. 8 is a diagram showing a typical pulse train pattern used forrecording data in a CD-R including a recording layer containing anorganic dye and shows a pulse train pattern for recording 3T to 11Tsignals in the EFM Modulation Code.

As shown in FIG. 8, in the case where data are to be recorded in a CD-R,a recording pulse having a width corresponding to the length of arecording mark M to be formed is generally employed (See Japanese PatentApplication Laid Open No. 2000-187842, for example).

More specifically, the power of a laser beam is fixed to a bottom powerPb when the laser beam is projected onto a blank region in which norecording mark M is formed and fixed to a recording power Pw when thelaser beam is projected onto a region in which a recording mark M is tobe formed. As a result, an organic dye contained in a recording layer isdecomposed or degraded at a region in which a recording mark M is to beformed and the region is physically deformed, thereby forming arecording mark M therein. In this specification, such a pulse trainpattern is called a single pulse pattern.

FIG. 9 is a diagram showing a typical pulse train pattern used forrecording data in a DVD-R including a recording layer containing anorganic dye and shows a pulse train pattern for recording a T signal inthe 8/16 Modulation Code.

Since data are recorded in a DVD-R at a higher linear recording velocitythan when recording data in a CD-R, unlike the case of recording data ina CD-R, it is difficult to form a recording mark having a good shapeusing a recording pulse having a width corresponding to the length ofthe recording mark M to be formed.

Therefore, data are recorded in a DVD-R using a pulse train in which, asshown in FIG. 9, the recording pulse is divided into a number of dividedpulses corresponding to the length of the recording mark M to be formed.

More specifically, in the case of recording an nT signal where n is aninteger equal to or larger than 3 and equal to or smaller than 11 or 14in the 8/16 Modulation Code, (n−2) divided pulses are employed and thepower of the laser beam is set to a recording power Pw at the peak ofeach of the divided pulses and set to a bottom power Pb at the otherportions of the pulse. In this specification, the thus constituted pulsetrain pattern is referred to as “a basic pulse train pattern”.

As shown in FIG. 9, in the basic pulse train pattern, the level of abottom power Pb is set to be equal to a reproducing power Pr used forreproducing data or close thereto.

On the other hand, a next-generation type optical recording medium thatoffers improved recording density and has an extremely high datatransfer rate has been recently proposed.

In such a next-generation type optical recording medium, in order toachieve an extremely high data transfer rate, it is required to recorddata at a higher linear recording velocity than that in a conventionaloptical recording medium, and since the recording power Pw necessary forforming a recording mark is generally substantially proportional to thesquare root of the linear recording velocity in a write-once opticalrecording medium, it is necessary to employ a semiconductor laser havinga high output for recording data in a next-generation optical recordingmedium.

Further, in the next-generation type optical recording medium, theachievement of increased recording capacity and extremely high datatransfer rate inevitably requires the diameter of the laser beam spotused to record and reproduce data to be reduced to a very small size.

In order to reduce the laser beam spot diameter, the numerical apertureof the objective lens for condensing the laser beam needs to beincreased to 0.7 or more, for example, to about 0.85, and the wavelengthof the laser beam needs to be shortened to 450 nm or less, for example,to about 400 nm.

However, the output of a semiconductor laser emitting a laser beamhaving a wavelength equal to or shorter than 450 nm is smaller than thatof a semiconductor laser emitting a laser beam having a wavelength of780 nm for a CD and that of a semiconductor laser emitting a laser beamhaving a wavelength of 650 nm for a DVD, and a semiconductor laser thatemits a laser beam having a wavelength equal to or shorter than 450 nmand has a high output is expensive.

These problems are particularly serious in a write-once type opticalrecording medium so constituted that elements contained in a pluralityof recording layers mix with each other by heat generated by a laserbeam projected thereonto, thereby forming a recording mark.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity using a laser beam having a low recording power.

It is another object of the present invention to provide a method forrecording data in an optical recording medium which can record data in awrite-once type optical recording medium at a high linear recordingvelocity using an inexpensive semiconductor laser having a low output.

It is a further object of the present invention to provide a method forrecording data in an optical recording medium which can record data in awrite-once type optical recording medium including two or more recordinglayers at a high linear recording velocity using a laser beam having alow recording power.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity using a laser beam having a low recording power.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity using an inexpensive semiconductor laser having a low output.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium including two or morerecording layers at a high linear recording velocity using a laser beamhaving a low recording power.

It is a further object of the present invention to provide an opticalrecording medium in which data can be recorded at a high linearrecording velocity using a laser beam having a low recording power.

It is a further object of the present invention to provide an opticalrecording medium in which data can be recorded at a high linearrecording velocity using an inexpensive semiconductor laser having a lowoutput.

It is a further object of the present invention to provide an opticalrecording medium including two or more recording layers in which datacan be recorded at a high linear recording velocity using a laser beamhaving a low recording power.

The inventors of the present invention vigorously pursued a study foraccomplishing the above objects and, as a result, made the discoverythat in order to record data in an optical recording medium at a highlinear recording velocity using a laser beam having a low recordingpower it was effective to increase a total amount of heat supplied forforming a recording mark by modulating the power of the laser beam usingthe single pulse pattern, but that in the case where the linearrecording velocity of data was low, if the total amount of heat suppliedfor forming a recording mark was increased by modulating the power ofthe laser beam using the single pulse pattern, the recording mark becamewider and cross-talk of data increased and that in the case of employinga pulse train pattern having a smaller number of pulses whose level wasset to a level corresponding to a recording power as the linearrecording velocity became higher and modulating the power of a laserbeam thereby to record data in a write-once type optical recordingmedium, it was possible to record data in the write-once type opticalrecording medium at a high linear recording velocity using a laser beamhaving a low recording power and it was possible to prevent cross-talkof data from increasing even when a linear recording velocity was low.

Therefore, the above objects of the present invention can beaccomplished by a method for recording data in an optical recordingmedium wherein data are recorded in a write-once type optical recordingmedium including at least one recording layer disposed on a substrate byprojecting a laser beam whose power is modulated in accordance with apulse train pattern including at least pulses whose levels are set tolevels corresponding to a recording power and a bottom power onto the atleast one recording layer and forming a recording mark in apredetermined region of the at least one recording layer, the method forrecording data in an optical recording medium comprising a step ofemploying a pulse train pattern having the smaller number of pulseswhose level is set to a level corresponding to a recording power as alinear recording velocity becomes higher and modulating the power of alaser beam thereby to form a recording mark in the predetermined regionof the at least one recording layer.

In this specification, in the case where an optical recording mediumincludes a recording layer containing an organic dye, a region in whichthe organic dye chemically changes or chemically and physically changesupon being irradiated with a laser beam is referred to as a “recordingmark” and in the case where an optical recording medium includes tworecording layers each containing an inorganic element as a primarycomponent, a region in which the inorganic elements contained in the tworecording layers as a primary component are mixed upon being irradiatedwith a laser beam is referred to as a “recording mark”.

According to the present invention, since data are recorded in apredetermined region of the at least one recording layer by employing apulse train pattern having the smaller number of pulses whose level isset to a level corresponding to a recording power as the linearrecording velocity becomes higher and modulating the power of a laserbeam thereby to form a recording mark in the predetermined region of theat least one recording layer, it is possible to record data in anoptical recording medium using a laser beam having a low recording powereven when the linear recording velocity is high and it is possible toprevent cross-talk of data from increasing even when the linearrecording velocity is low. Therefore, it is possible to employ asemiconductor laser having a relatively low output even when data arerecorded at a high linear recording velocity.

Further, according to the present invention, data can be recorded usinga laser beam having substantially the same recording power even atdifferent linear recording velocities.

In a preferred aspect of the present invention, the number of pulses isset to 1 in the case where data are to be recorded at a linear recordingvelocity equal to or higher than a first linear recording velocity VH.

In a preferred aspect of the present invention, in the case where dataare to be recorded at a linear recording velocity VM lower than thefirst linear recording velocity VH and higher than a second linearrecording velocity VL, the number of pulses is set to 1 at least whenthe shortest recording mark is to be formed and the number of pulses isset larger as a length of the recording mark to be formed becomeslonger.

In a preferred aspect of the present invention, in the case where dataare to be recorded at a linear recording velocity lower than the firstlinear recording velocity VH and higher than a second linear recordingvelocity VL, the number of pulses is set to 1 at least when the shortestrecording mark is to be formed and the number of pulses is set larger asthe linear recording velocity VM becomes lower.

In a preferred aspect of the present invention, in the case where dataare to be recorded by forming recording marks having respective lengthsat a linear recording velocity, the number of pulses is set so that adifference between itself and the number representing a length of arecording mark is constant.

In a further preferred aspect of the present invention, the first linearrecording velocity is determined to be equal to or higher than 10 m/sec.

In a further preferred aspect of the present invention, the bottom poweris set to a higher level as the linear recording velocity becomeshigher.

In a further preferred aspect of the present invention, a ratio of thebottom power to the recording power is set higher as the linearrecording velocity becomes higher.

In a further preferred aspect of the present invention, data arerecorded in the optical recording medium by projecting a laser beamhaving a wavelength equal to or shorter than 450 nm thereonto.

In a further preferred aspect of the present invention, data arerecorded in the optical recording medium by employing an objective lensand a laser beam whose numerical aperture NA and wavelength λ satisfyλ/NA≦640 nm, and projecting the laser beam onto the optical recordingmedium via the objective lens.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatthe at least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.

In a further preferred aspect of the present invention, the secondrecording layer is formed so as to be in contact with the firstrecording layer.

The above objects of the present invention can be also accomplished by amethod for recording data in an optical recording medium wherein dataare recorded in a write-once type optical recording medium including atleast one recording layer disposed on a substrate by projecting a laserbeam whose power is modulated in accordance with a pulse train patternincluding at least pulses whose levels are set to levels correspondingto a recording power and a bottom power onto the at least one recordinglayer and forming a recording mark in a predetermined region of the atleast one recording layer, the method for recording data in an opticalrecording medium comprising a step of employing a pulse train patternhaving a smaller number of pulses whose level is set to a levelcorresponding to a recording power as a ratio of a track pitch TP of theoptical recording medium to a diameter of a spot of the laser beambecomes smaller and modulating the power of a laser beam thereby to forma recording mark in the predetermined region of the at least onerecording layer.

The above objects of the present invention can be also accomplished byan apparatus for recording data in an optical recording medium whereindata are recorded in a write-once type optical recording mediumincluding at least one recording layer disposed on a substrate byprojecting a laser beam whose power is modulated in accordance with apulse train pattern including at least pulses whose levels are set tolevels corresponding to a recording power and a bottom power onto the atleast one recording layer and forming a recording mark in apredetermined region of the at least one recording layer, the apparatusfor recording data in an optical recording medium being constituted soas to employ a pulse train pattern having a smaller number of pulseswhose level is set to a level corresponding to a recording power as alinear recording velocity becomes higher and modulate the power of alaser beam thereby to form a recording mark in the predetermined regionof the at least one recording layer.

According to the present invention, the apparatus for recording data inan optical recording medium is constituted so as to employ a pulse trainpattern having a smaller number of pulses whose level is set to a levelcorresponding to a recording power as the linear recording velocitybecomes higher and modulate the power of a laser beam thereby to form arecording mark in the predetermined region of the at least one recordinglayer, so that it is possible to record data in an optical recordingmedium using a laser beam having a low recording power even when thelinear recording velocity is high and it is possible to preventcross-talk of data from increasing even when the linear recordingvelocity is low. Therefore, it is possible to employ a semiconductorlaser having a relatively low output even when data are recorded at ahigh linear recording velocity.

In a preferred aspect of the present invention, the number of pulses isset to 1 in the case where data are to be recorded at a linear recordingvelocity equal to or higher than a first linear recording velocity VH.

In a preferred aspect of the present invention, in the case where dataare to be recorded at a linear recording velocity VM lower than thefirst linear recording velocity VH and higher than a second linearrecording velocity VL, the number of pulses is set to 1 at least whenthe shortest recording mark is to be formed and the number of pulses isset larger as the length of a recording mark to be formed becomeslonger.

In a preferred aspect of the present invention, in the case where dataare to be recorded at a linear recording velocity lower than the firstlinear recording velocity VH and higher than a second linear recordingvelocity VL, the number of pulses is set to 1 at least when the shortestrecording mark is to be formed and the number of pulses is set larger asthe linear recording velocity VM becomes lower.

In a preferred aspect of the present invention, in the case where dataare to be recorded by forming recording marks having respective lengthsat a linear recording velocity, the number of pulses is set so that adifference between itself and the number representing a length of arecording mark is constant.

In a further preferred aspect of the present invention, the first linearrecording velocity is determined to be equal to or higher than 10 m/sec.

The above and other objects of the present invention can be alsoaccomplished by a write-once type optical recording medium comprising asubstrate and at least one recording layer disposed on the substrate andbeing constituted so that data are recorded by projecting a laser beamwhose power is modulated in accordance with a pulse train patternincluding at least pulses whose levels are set to levels correspondingto a recording power and a bottom power onto the at least one recordinglayer and forming a recording mark in the at least one recording layer,the optical recording medium being recorded with data for settingrecording conditions necessary for employing a pulse train patternhaving a smaller number of pulses whose level is set to a levelcorresponding to a recording power as a linear recording velocitybecomes higher and modulating the power of a laser beam thereby.

According to the present invention, since it is possible to record datain an optical recording medium by reading data for setting recordingconditions recorded in the optical recording medium when data are to berecorded in the optical recording medium, employing a pulse trainpattern having a smaller number of pulses whose level is set to a levelcorresponding to a recording power as the linear recording velocitybecomes higher and modulating the power of a laser beam thereby to form,it is possible to record data in an optical recording medium using alaser beam having a low recording power even when the linear recordingvelocity is high and it is possible to prevent cross-talk of data fromincreasing even when the linear recording velocity is low. Therefore, itis possible to employ a semiconductor laser having a relatively lowoutput even when data are recorded at a high linear recording velocity.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatthe at least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.

In a further preferred aspect of the present invention, the secondrecording layer is formed so as to be in contact with the firstrecording layer.

In the present invention, it is preferable for the first recording layerand the second recording layer to contain different elements as aprimary component and for each of them to contain an element selectedfrom a group consisting of Al, Si, Ge, C, Sn, Au, Zn, Cu, B, Mg, Ti, Mn,Fe, Ga, Zr, Ag and Pt as a primary component.

In a preferred aspect of the present invention, the first recordinglayer contains an element selected from a group consisting of Si, Ge,Sn, Mg, In, Zn, Bi and Al as a primary component, and the secondrecording layer contains Cu as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, Sn, Mg,In, Zn, Bi and Al as a primary component, and the second recording layercontains Cu as a primary component, the optical recording medium mayinclude one or more recording layers containing an element selected fromthe group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Al as a primarycomponent or one or more recording layers containing Cu as a primaryelement, in addition to the first recording layer and the secondrecording layer.

In the present invention, it is more preferable for the first recordinglayer to contain an element selected from a group consisting of Ge, Si,Mg, Al and Sn as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, Sn, Mg,In, Zn, Bi and Al as a primary component, and the second recording layercontains Cu as a primary component, it is preferable that at least onekind of an element selected from the group consisting of Al, Si, Zn, Mg,Au, Sn, Ge, Ag, P, Cr, Fe and Ti is added to the second recording layerand it is more preferable that at least one kind of an element selectedfrom the group consisting of Al, Zn, Sn and Au is added to the secondrecording layer.

In another preferred aspect of the present invention, the firstrecording layer contains an element selected from a group consisting ofSi, Ge, C, Sn, Zn and Cu as a primary component and the second recordinglayer contains Al as a primary component.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, the optical recording medium may include oneor more recording layer containing an element selected from the groupconsisting of Si, Ge, C, Sn, Zn and Cu as a primary component or one ormore recording layer containing Al as a primary component, in additionto the first recording layer and the second recording layer.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, it is preferable that at least one kind of anelement selected from the group consisting of Mg, Au, Ti and Cu is addedto the second recording layer.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, the first recording layer and the secondrecording layer are preferably formed so that the total thicknessthereof is 2 nm to 40 nm, more preferably, 2 nm to 30 nm, mostpreferably, 2 nm to 20 nm.

In a further preferred aspect of the present invention, the firstrecording layer contains an element selected from a group consisting ofSi, Ge, C and Al as a primary component, the second recording layercontains Zn as a primary component and the first recording layer and thesecond recording layer are formed so that the total thickness thereof isequal to or thinner than 30 nm.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, the optical recording medium may include one or morerecording layer containing an element selected from the group consistingof Si, Ge, C and Al as a primary component or one or more recordinglayer containing Zn as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, it is preferable for the first recording layer tocontain an element selected from a group consisting of Si, Ge and C as aprimary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, the first recording layer and the second recordinglayer are preferably formed so that the total thickness thereof is 2 nmto 30 nm, more preferably, 2 nm to 24 nm, most preferably, 2 nm to 12nm.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, it is preferable that at least one kind of an elementselected from the group consisting of Mg, Cu and Al I added to thesecond recording layer.

In a preferred aspect of the present invention, the light transmissionlayer is formed so as to have a thickness of 10 nm to 300 nm.

The above and other objects and features of the present invention willbecome apparent from the following description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing the structure of anoptical recording medium that is a preferred embodiment of the presentinvention.

FIG. 2( a) is a schematic enlarged cross-sectional view of the opticalrecording medium shown in FIG. 1 and FIG. 2( b) is a schematic enlargedcross-sectional view showing an optical recording medium after data havebeen recorded therein.

FIG. 3 is a table showing how the number of pulses of a pulse trainpattern for modulating the power of a laser beam and linear recordingvelocity are related to the length of a recording mark to be formedusing the 1,7RLL Modulation Code.

FIG. 4 is a set of diagrams showing pulse train patterns used forrecording data in an optical recording medium at a first linearrecording velocity VL, wherein FIG. 4( a) shows a pulse train patternused for recording a 2T signal and FIG. 4( b) shows a pulse trainpattern used for recording one of a 3T signal to an 8T signal.

FIG. 5 is a diagram showing a pulse train patterns used for recordingdata, namely, one of a 2T signal to an 8T signal in an optical recordingmedium at a third linear recording velocity VH.

FIG. 6 is a set of diagrams showing pulse train patterns used forrecording data in an optical recording medium at a second linearrecording velocity VM higher than a first linear recording velocity VLand lower than a third linear recording velocity VH, wherein FIG. 6( a)shows a pulse train pattern used for recording one of a 2T signal to a5T signal and FIG. 6( b) shows a pulse train pattern used for recordingone of a 6T signal to an 8T signal.

FIG. 7 is a block diagram showing a data recording and reproducingapparatus that is a preferred embodiment of the present invention.

FIG. 8 is a diagram showing a typical pulse train pattern used forrecording data in a CD-R including a recording layer containing anorganic dye and shows a pulse train pattern for recording one of a 3Tsignal to an 11T signal in the EFM Modulation Code.

FIG. 9 is a diagram showing a typical pulse train pattern (basic pulsetrain pattern) used for recording data in a DVD-R including a recordinglayer containing an organic dye and shows a pulse train pattern forrecording a 7T signal in the 8/16 Modulation Code.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing the structure of anoptical recording medium that is a preferred embodiment of the presentinvention.

As shown in FIG. 1, the optical recording medium 10 according to thisembodiment is constituted as a write-once type optical recording mediumand includes a substrate 11, a reflective layer 12 formed on the surfaceof the substrate 11, a second dielectric layer 13 formed on the surfaceof the reflective layer 12, a second recording layer 32 formed on thesurface of the second dielectric layer 13, a first recording layer 31formed on the surface of the second recording layer 32, a firstdielectric layer 15 formed on the surface of the first recording layer31 and a light transmission layer 16 formed on the surface of the firstdielectric layer 15.

As shown in FIG. 1, a center hole is formed at a center portion of theoptical recording medium 10.

In this embodiment, as shown in FIG. 1, a laser beam L10 is projectedonto the surface of the light transmission layer 16, thereby recordingdata in the optical recording medium 10 or reproducing data from theoptical recording medium 10.

The substrate 11 serves as a support for ensuring mechanical strengthrequired for the optical recording medium 10.

The material used to form the substrate 11 is not particularly limitedinsofar as the substrate 11 can serve as the support of the opticalrecording medium 10. The substrate 11 can be formed of glass, ceramic,resin or the like. Among these, resin is preferably used for forming thesubstrate 11 since resin can be easily shaped. Illustrative examples ofresins suitable for forming the substrate 40 include polycarbonateresin, acrylic resin, epoxy resin, polystyrene resin, polyethyleneresin, polypropylene resin, silicone resin, fluoropolymers,acrylonitrile butadiene styrene resin, urethane resin and the like.Among these, polycarbonate resin is most preferably used for forming thesubstrate 11 from the viewpoint of easy processing, opticalcharacteristics and the like.

In this embodiment, the substrate 11 has a thickness of about 1.1 mm.

The shape of the substrate 11 is not particularly limited but isnormally disk-like, card-like or sheet-like.

As shown in FIG. 1, grooves 1 a and lands 11 b are alternately formed onthe surface of the substrate 11. The grooves 11 a and/or lands 11 bserve as a guide track for the laser beam L10 when data are to berecorded or when data are to be reproduced.

The reflective layer 12 serves to reflect the laser beam L10 enteringthrough the light transmission layer 16 so as to emit it from the lighttransmission layer 16.

The thickness of the reflective layer 12 is not particularly limited butis preferably from 10 nm to 300 nm, more preferably from 20 nm to 200nm.

The material used to form the reflective layer 12 is not particularlylimited insofar as it can reflect a laser beam, and the reflective layer12 can be formed of Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ge, Ag, Pt, Auand the like. Among these materials, it is preferable to form thereflective layer 12 of a metal material having a high reflectivity, suchas Al, Au, Ag, Cu or alloy containing at least one of these metals, suchas alloy of Al and Ti.

The reflective layer 12 is provided in order to increase the differencein reflection coefficient between a recorded region and an unrecordedregion by a multiple interference effect when the laser beam L10 is usedto optically reproduce data from the first recording layer 31 and thesecond recording layer 32, thereby obtaining a higher reproduced signal(C/N ratio).

The first dielectric layer 15 and the second dielectric layer 13 serveto protect the first recording layer 31 and the second recording layer32. Degradation of optically recorded data can be prevented over a longperiod by the first dielectric layer 15 and the second dielectric layer13. Further, since the second dielectric layer 13 also serves to preventthe substrate 11 and the like from being deformed by heat, it ispossible to effectively prevent jitter and the like from becoming worsedue to the deformation of the substrate 11 and the like.

The dielectric material used to form the first dielectric layer 15 andthe second dielectric layer 13 is not particularly limited insofar as itis transparent and the first dielectric layer 15 and the seconddielectric layer 13 can be formed of a dielectric material containingoxide, sulfide, nitride or a combination thereof, for example, as aprimary component. More specifically, in order to prevent the substrate11 and the like from being deformed by heat and thus protect the firstrecording layer 31 and the second recording layer 32, it is preferablefor the first dielectric layer 15 and the second dielectric layer 13 tocontain at least one kind of dielectric material selected from the groupconsisting of Al₂O₃, AIN, ZnO, ZnS, GeN, GeCrN, CeO, SiO, SiO₂, SiN andSiC as a primary component and it is more preferable for the firstdielectric layer 15 and the second dielectric layer 13 to containZnS.SiO₂ as a primary component.

The first dielectric layer 15 and the second dielectric layer 13 may beformed of the same dielectric material or of different dielectricmaterials. Moreover, at least one of the first dielectric layer 15 andthe second dielectric layer 13 may have a multi-layered structureincluding a plurality of dielectric films.

In this specification, the statement that a dielectric layer contains acertain dielectric material as a primary component means that thedielectric material is maximum among dielectric materials contained inthe dielectric layer. ZnS.SiO₂ means a mixture of ZnS and SiO₂.

The thickness of the first dielectric layer 15 and the second dielectriclayer 13 is not particularly limited but is preferably from 3 nm to 200nm. If the first dielectric layer 15 or the second dielectric layer 13is thinner than 3 nm, it is difficult to obtain the above-describedadvantages. On the other hand, if the first dielectric layer 15 or thesecond dielectric layer 13 is thicker than 200 nm, it takes a long timeto form the first dielectric layers 15 and the second dielectric layers13, thereby lowering the productivity of the optical recording medium10, and cracks may be generated in the optical recording medium 10 owingto stress present in the first dielectric layers 15 and/or the seconddielectric layer 13.

The first recording layer 31 and the second recording layer 32 areadapted for recording data therein. In this embodiment, the firstrecording layer 31 is disposed on the side of the light transmissionlayer 16 and the second recording layer 32 is disposed on the side ofthe substrate 11.

In this embodiment, the first recording layer 31 contains an elementselected from the group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Alas a primary component and the second recording layer 32 contains Cu asa primary component.

It is possible to improve the long term storage reliability of anoptical recording medium 10 by proving the first recording layer 31containing an element selected from the group consisting of Si, Ge, Sn,Mg, In, Zn, Bi and Al as a primary component and the second recordinglayer 32 containing Cu as a primary component in this manner.

Further, these elements apply only light load to the environment andthere is no risk of the global atmosphere being damaged.

In order to thoroughly improve the C/N ratio of the reproduced signal,it is particularly preferable for the first recording layer 31 tocontain an element selected from the group consisting of Ge, Si, Mg, Aland Sn as a primary component and is particularly preferable for the tocontain Si as a primary component.

Cu contained in the second recording layer 32 as a primary componentquickly mixes with the element contained in the first recording layer 31when irradiated with a laser beam L10, thereby enabling data to bequickly recorded in the first recording layer 31 and the secondrecording layer 32.

In order to improve the recording sensitivity of the first recordinglayer 31, it is preferable for the first recording layer 31 to be addedwith at least one kind of an element selected from the group consistingof Mg, Al, Cu, Ag and Au.

In order to improve the storage reliability and the recordingsensitivity of the second recording layer 32, it is preferable for thesecond recording layer 32 to be added with at least one kind of anelement selected from the group consisting of Al, Si, Zn, Mg, Au, Sn,Ge, Ag, P, Cr, Fe and Ti.

The total thickness of the first recording layer 31 and the secondrecording layer 32 is not particularly limited but the surfacesmoothness of the first recording layer 31 irradiated with the laserbeam L10 becomes worse as the total thickness of the first recordinglayer 31 and the second recording layer 32 becomes thicker. As a result,the noise level of the reproduced signal becomes higher and therecording sensitivity is lowered. On the other hand, in the case wherethe total thickness of the first recording layer 31 and the secondrecording layer 32 is too small, the change in reflection coefficientbetween before and after irradiation with the laser beam L10 is small,so that a reproduced signal having high strength (C/N ratio) cannot beobtained. Moreover, it becomes difficult to control the thickness of thefirst recording layer 31 and the second recording layer 32.

Therefore, in this embodiment, the first recording layer 31 and thesecond recording layer 32 are formed so that the total thickness thereofis from 2 nm to 40 nm. In order to obtain a reproduced signal havinghigher strength (C/N ratio) and further decrease the noise level of thereproduced signal, the total thickness of the first recording layer 31and the second recording layer 32 is preferably from 2 nm to 20 nm andmore preferably 2 nm to 10 nm.

The individual thicknesses of the first recording layer 31 and thesecond recording layer 32 are not particularly limited but in order toconsiderably improve the recording sensitivity and greatly increase thechange in reflection coefficient between before and after irradiationwith the laser beam L10, the thickness of the first recording layer 31is preferably from 1 nm to 30 nm and the thickness of the secondrecording layer 32 is preferably from 1 nm to 30 nm. Further, it ispreferable to define the ratio of the thickness of the first recordinglayer 31 to the thickness of the second recording layer 32 (thickness offirst recording layer 31/thickness of second recording layer 32) to befrom 0.2 to 5.0.

The light transmission layer 16 serves to transmit a laser beam L10 andpreferably has a thickness of 10 μm to 300 μm. More preferably, thelight transmission layer 16 has a thickness of 50 μm to 150 μm.

The material used to form the light transmission layer 16 is notparticularly limited but in the case where the light transmission layer16 is to be formed by the spin coating process or the like, ultravioletray curable resin, electron beam curable resin or the like is preferablyused. More preferably, the light transmission layer 16 is formed ofultraviolet ray curable resin.

The light transmission layer 16 may be formed by adhering a sheet madeof light transmittable resin to the surface of the first dielectriclayer 15 using an adhesive agent.

The optical recording medium 10 having the above-described configurationcan, for example, be fabricated in the following manner.

The reflective layer 12 is first formed on the surface of the substrate11 formed with the grooves 11 a and lands 11 b.

The reflective layer 12 can be formed by a gas phase growth processusing chemical species containing elements for forming the reflectivelayer 12. Illustrative examples of the gas phase growth processesinclude vacuum deposition process, sputtering process and the like.

The second dielectric layer 13 is then formed on surface of thereflective layer 12.

The second dielectric layer 13 can be also formed by a gas phase growthprocess using chemical species containing elements for forming thesecond dielectric layer 13. Illustrative examples of the gas phasegrowth processes include vacuum deposition process, sputtering processand the like.

The second recording layer 32 is further formed on the second dielectriclayer 13. The second recording layer 32 can be also formed by a gasphase growth process using chemical species containing elements forforming the second recording layer 32.

The first recording layer 31 is then formed on the second recordinglayer 32. The first recording layer 31 can be also formed by a gas phasegrowth process using chemical species containing elements for formingthe first recording layer 31.

The first dielectric layer 15 is then formed on the first recordinglayer 31. The first dielectric layer 15 can be also formed by a gasphase growth process using chemical species containing elements forforming the first dielectric layer 15.

Finally, the light transmission layer 16 is formed on the firstdielectric layer 15. The light transmission layer 16 can be formed, forexample, by applying an acrylic ultraviolet ray curable resin or epoxyultraviolet ray curable resin adjusted to an appropriate viscosity ontothe surface of the second dielectric layer 15 by spin coating to form acoating layer and irradiating the coating layer with ultraviolet rays tocure the coating layer.

Thus, the optical recording medium 10 was fabricated.

Data are recorded in the optical recording medium 10 of theabove-described configuration, in the following manner, for example.

As shown in FIGS. 1 and 2( a), the first recording layer 31 and thesecond recording layer 32 are first irradiated via the lighttransmission layer 16 with a laser beam L10 having predetermined power.

In order to record data with high recording density, it is preferable toproject a laser beam L10 having a wavelength A of 450 nm or shorter ontothe optical recording medium 10 via an objective lens (not shown) havinga numerical aperture NA of 0.7 or more and it is more preferable thatA/NA be equal to or smaller than 640 nm. In such a case, the spotdiameter of the laser beam L10 on the surface of the first recordinglayer 31 becomes equal to or smaller than 0.65 μm.

In this embodiment, a laser beam L10 having a wavelength λ of 405 nm iscondensed onto the optical recording medium 10 via an objective lenshaving a numerical aperture NA of 0.85 so that the spot diameter of thelaser beam L10 on the surface of the first recording layer 31 becomesabout 0.43 μm.

As a result, the element contained in the first recording layer 31 as aprimary component and the element contained in the second recordinglayer 32 as a primary component mix with each other and as shown in FIG.2( b), a recording mark M composed of a mixture of the primary componentelement of the first recording layer 31 and the primary componentelement of the second recording layer 32 is formed.

When the primary component elements of the first recording layers 31 and32 are mixed, the reflection coefficient of the region markedly changes.Since the reflection coefficient of the thus formed recording mark M istherefore greatly different from that of the region surrounding themixed region M, it is possible to obtain a high reproduced signal (C/Nratio) when optically recorded information is reproduced.

When the laser beam L10 is projected, the first recording layer 31 andthe second recording layer 32 are heated by the laser beam L10. In thisembodiment, however, the first dielectric layer 15 and the seconddielectric layer 13 are disposed outward of the first recording layer 31and the second recording layer 32. Deformation of the substrate 11 andthe light transmission layer 16 by heat is therefore effectivelyprevented.

In the case where data are to be recorded in an optical recording medium10 by projecting a laser beam L10 thereonto, the power of the laser beamL10 is modulated in accordance with a pulse train pattern includingpulses whose levels are set to a recording power Pw and a bottom powerPb.

In a next-generation type optical recording medium 10 shown in FIGS. 1and 2, it is required to record data at a high linear recording velocityand in a write-once type optical recording medium, a recording power Pwnecessary for forming a recording mark is substantially proportional tothe square root of the linear recording velocity. Therefore, it isnecessary to set the recording power Pw of a pulse train pattern to ahigh level in order to record data in the optical recording medium 10 ata high linear recording velocity.

However, since the output of a semiconductor laser adapted for emittinga laser beam having a wavelength equal to or shorter than 450 nm andused for recording data in the next-generation type optical recordingmedium 10 is low and a semiconductor laser having a high output isexpensive, even in the case where data are to be recorded in the opticalrecording medium 10 at a high linear recording velocity, it is necessaryto select a pulse train pattern that enables data to be recorded thereinat the lowest linear recording velocity possible.

In a study done by the inventors of the present invention, it was foundthat it was effective to increase the total amount of heat supplied forforming a recording mark M by modulating the power of the laser beam L10using the single pulse pattern in order to record data in the opticalrecording medium 10 at a high linear recording velocity using a laserbeam having a low recording power but that in the case where the linearrecording velocity of data was low, if a recording mark was formed bymodulating the power of the laser beam L10 using a single pulse pattern,the total amount of heat supplied for forming a recording mark becameexcessive and the recording mark became wider, whereby cross-talk ofdata increased. It was further found that this tendency becamepronounced as the length of the recording mark became longer.

Therefore, in this embodiment, a pulse train pattern having a smallernumber of pulses whose level is set to a level corresponding to arecording power Pw is employed as the linear recording velocity of datais higher, thereby modulating the power of a laser beam L10 to form arecording mark.

Concretely, in the case of employing the 1,7RLL Modulating Code, asshown in FIG. 3, the number of pulses of the pulse train pattern isselected in accordance with the linear recording velocity and the lengthof the recording mark M to be formed.

More specifically, as shown in FIG. 3, in the case where data are to berecorded in the optical recording medium 10 at a first linear recordingvelocity VL which is low, the basic pulse train pattern is selected asthe pulse train pattern for modulating the power of the laser beam L10and when an nT signal is to be recorded where n is an integer of 2 to 8in the 1,7RLL Modulation Code, the basic pulse train pattern including(n−1) divided pulses is employed. In the case where a 2T signal is to berecorded, the number of the divided pulses becomes 1 and the basic pulsetrain pattern has the same pattern as that of the single pulse pattern.

To the contrary, in the case where data are to be recorded in theoptical recording medium 10 at a third linear recording velocity VHwhich is high, the single pulse pattern is selected as the pulse trainpattern for modulating the power of the laser beam L10. Here, the firstlinear recording velocity VL and the third linear recording velocity VHpreferably are such that 2*VL is equal to or lower than VH and morepreferably are such that 4*VL is equal to or lower than VH. Further, thethird linear recording velocity VH is preferably equal to or higher than10 m/sec and more preferably is equal to or higher than 20 m/sec.

On the other hand, in the case where data are to be recorded in theoptical recording medium 10 at a second linear recording velocity VMhigher than the first linear recording velocity VL and lower than thethird linear recording velocity VH, the single pulse pattern is selectedas the pulse train pattern for modulating the power of the laser beamL10 when the recording mark M to be formed is short, while the basicpulse train pattern is selected as the pulse train pattern formodulating the power of the laser beam L10 when the recording mark M tobe formed is long.

Further, in the case where a recording mark M having the same length isto be formed in the optical recording medium 10 at a second linearrecording velocity VM higher than the first linear recording velocity VLand lower than the third linear recording velocity VH, the pulse trainpattern is determined so that the number of pulses included in the pulsetrain pattern is larger as the linear recording velocity VM becomeslower and on the other hand, when the linear recording velocity VM isthe same in the case where a recording mark M having the same length isto be formed in the optical recording medium 10 at a second linearrecording velocity VM higher than the first linear recording velocity VLand lower than the third linear recording velocity VH, the pulse trainpattern is determined so that the number of pulses included in the pulsetrain pattern is larger as the recording mark becomes longer.

In this embodiment, the basic pulse train pattern includes not only thebasic pulse train pattern shown in FIG. 9 and including (n−1) dividedpulses but also a basic pulse train pattern including n or (n−2) dividedpulses. It is preferable to employ a basic pulse train pattern including(n−2) divided pulses in the 8/16 Modulation Code and employ a pulsetrain pattern including (n−1) divided pulses in the 1,7RLL ModulationCode.

FIG. 4 is a set of diagrams showing pulse train patterns used forrecording data in an optical recording medium at the first linearrecording velocity VL, wherein FIG. 4( a) shows a pulse train patternused for recording a 2T signal and FIG. 4( b) shows a pulse trainpattern used for recording one of a 3T signal to an 8T signal.

As shown in FIG. 4( a) and FIG. 4( b), in the case where data are to berecorded in the optical recording medium 10 at the first linearrecording velocity VL, the recording pulse for forming a recording markM is divided into (n−1) divided pulses and the power of the laser beamL10 is set to a recording power PwL at the peak of each of the dividedpulses and set to a bottom power PbL at the other portions of the pulse.

In this manner, in the case where data are to be recorded in the opticalrecording medium 10 at the first linear recording velocity VL, since therecording pulse for forming the recording mark M is divided into (n−1)divided pulses and the power of the laser beam L10 is set to a recordingpower PWL at the peak of each of the divided pulses and set to a bottompower PbL at the other portions of the pulse, it is possible to preventa total amount of heat supplied for forming the recording mark M frombecoming excessive and it is therefore possible to effectively preventthe recording mark from becoming wider and cross-talk of data fromincreasing.

The recording power PwL is set to a high level at which the elementcontained in the first recording layer 31 as a primary component and theelement contained in the second recording layer 32 as a primarycomponent can be heated and mixed to form a record mark M when a laserbeam having the recording power PwL is projected onto the opticalrecording medium 10. On the other hand, the first bottom power PbL isset to a low level at which the element contained in the first recordinglayer 31 as a primary component and the element contained in the secondrecording layer 32 as a primary component cannot substantially be mixedeven when a laser beam having the first bottom power PbL is projectedonto the optical recording medium 10.

Further, as shown in FIG. 4( a) and FIG. 4( b), the bottom power PbL isset to a level higher than a reproducing power Pr.

If the level of the bottom power PbL is set to a higher level than thereproducing power Pr in this manner, it is possible to augment theheating of the recording layer by the laser beam L10 having therecording power PwL by the laser beam L10 having the bottom power PbLand the recording power PWL can be therefore set to a low level.

FIG. 5 is a diagram showing a pulse train patterns used for recordingdata, namely one of a 2T signal to an 8T signal in the optical recordingmedium 10 at the third linear recording velocity VH.

As shown in FIG. 5, in the case where data are to be recorded in theoptical recording medium 10 at the third linear recording velocity VH,the single pulse train pattern is selected as a pulse train pattern formodulating the power of the laser beam L10 and the power of the laserbeam L10 is set to a recording layer PwH at regions where recordingmarks M are to be formed and set to a bottom power PbH at other portionsof the pulse.

Therefore, since the total amount of heat supplied for forming arecording mark M can be increased, it is possible to set the recordinglayer PwH to a low level.

The recording power PwH is set to a high level at which the elementcontained in the first recording layer 31 as a primary component and theelement contained in the second recording layer 32 as a primarycomponent can be heated and mixed to form a record mark M when a laserbeam having the recording power PwH is projected onto the opticalrecording medium 10. On the other hand, the first bottom power PbH isset to a low level at which the element contained in the first recordinglayer 31 as a primary component and the element contained in the secondrecording layer 32 as a primary component cannot substantially be mixedeven when a laser beam having the first bottom power PbH is projectedonto the optical recording medium 10.

The bottom power PbH is set to a level higher than a reproducing powerPr. If the level of the bottom power PbH is set to a higher level thanthe reproducing power Pr in this manner, it is possible to augment theheating of the recording layer by the laser beam L10 having therecording power PWH by the laser beam L10 having the bottom power PbHand the recording power PwH can be therefore set to a low level.

FIG. 6 is a set of diagrams showing pulse train patterns used forrecording data in the optical recording medium 10 at the second linearrecording velocity VM higher than the first linear recording velocity VLand lower than the third linear recording velocity VH, wherein FIG. 6(a) shows a pulse train pattern used for recording one of a 2T signal toa 5T signal and FIG. 6( b) shows a pulse train pattern used forrecording one of a 6T signal to an 8T signal.

As shown in FIG. 6( a), in the case where data are to be recorded in theoptical recording medium 10 at the second linear recording velocity VMlower than the third linear recording velocity VH, the single pulsepattern is selected as a pulse train pattern for modulating the power ofthe laser beam L10 when one of a 2T signal to a 5T signal is to berecorded and the basic pulse train pattern including 2 to 4 dividedpulses is selected when one of a 6T signal to an 8T signal is to berecorded. In these cases, the power of the laser beam L10 is modulatedso as to be equal to a recording power PwM at the peak of the singlepulse or each of the divided pulses and equal to a bottom power PbM atother portions of the pulse.

If a pulse train pattern for modulating the power of the laser beam L10is determined in this manner, when one of a 2T signal to a 5T signal isto be recorded, since the total amount of heat supplied for forming arecording mark M becomes large, it is possible to set the recordingpower PwM to a low level. On the other hand, since it is possible toprevent the total amount of heat supplied for forming a recording mark Mfrom becoming excessive, it is possible to effectively prevent a longrecording mark M formed using one of a 6T signal to an 8T signal frombecoming wider and cross-talk of data from increasing.

The recording power PwM is set to a high level at which the elementcontained in the first recording layer 31 as a primary component and theelement contained in the second recording layer 32 as a primarycomponent can be heated and mixed to form a record mark M when a laserbeam having the recording power PwM is projected onto the opticalrecording medium 10. On the other hand, the first bottom power PbM isset to a low level at which the element contained in the first recordinglayer 31 as a primary component and the element contained in the secondrecording layer 32 as a primary component cannot substantially be mixedeven when a laser beam having the first bottom power PbM is projectedonto the optical recording medium 10.

The bottom power PbM is set to a level higher than a reproducing powerPr. If the level of the bottom power PbM is set to a higher level thanthe reproducing power Pr in this manner, it is possible to augment theheating of the recording layer by the laser beam L10 having therecording power PWM by the laser beam L10 having the bottom power PbMand the recording power PwM can be therefore set to a low level.

It is preferable for the bottom power PbL of the pulse train patternused for recording data at the first linear recording velocity VL, thebottom power PbH of the pulse train pattern used for recording data atthe third linear recording velocity VH and the bottom power PbM of thepulse train pattern used for recording data at the second linearrecording velocity VM to be such that PbL is lower than PbM and PbM isequal to or lower than PbH, more preferable for them to be such that3*PbL is equal to or lower than PbM and PbM is equal to or lower thanPbH and most preferable for them to be such that 5*PbL is equal to orlower than PbM and PbM is lower than PbH.

Further, it is preferable to determine the pulse train patterns so thata ratio (PbL/PwL) of the bottom power PbL to the recording power PwL ofthe pulse train pattern used for recording data at the first linearrecording velocity VL, a ratio (PbH/PwH) of the bottom power PbH to therecording power PwH of the pulse train pattern used for recording dataat the third linear recording velocity VH and a ratio (PbM/PwM) of thebottom power PbM to the recording power PwM of the pulse train patternused for recording data at the second linear recording velocity VM aresuch that (PbL/PwL) is lower than (PbM/PwM) and (PbM/PwM) is equal to orlower than (PbH/PwH) and it is more preferable for the ratios to be suchthat 3*(PbL/PwL) is equal to or lower than (PbM/PwM) and (PbM/PwM) isequal to or lower than (PbH/PwH) and most preferable for the ratios tobe such that 5*(PbL/PwL) is equal to or lower than (PbM/PwM) and(PbM/PWM) is equal to or lower than (PbH/PwH).

In the case where the recording powers and the bottom powers of thepulse train patterns used for modulating the power of a laser beam areset in this manner, when data are to be recorded at different linearrecording velocities in a (multi-velocity recording) system in whichdata can be recorded by selecting a desired linear recording velocityselected from among a plurality of linear recording velocities, it ispossible to set the recording powers to substantially the same level.

Therefore, in this embodiment, since it is possible to set the recordingpower PwM to a low level and set recording powers to substantially thesame level in the case of recording data at different linear recordingvelocities, it is possible to employ a relatively inexpensivesemiconductor laser having a low output.

According to this embodiment, since the single pulse pattern is selectedas the pulse train pattern for modulating the power of the laser beamL10 in the case where data are to be recorded at the third linearrecording velocity VH, which is high, it is possible to increase thetotal amount of heat supplied for forming a recording mark M and it istherefore possible to record data in the optical recording medium 10with the recording power PwH set to a lower level.

Further, according to this embodiment, in the case where data are to berecorded at the first linear recording velocity VL, which is low, sincethe basic pulse train pattern is selected as the pulse train pattern formodulating the power of a laser beam L10 and the basic pulse trainpattern including (n−1) divided pulses when an nT signal is to berecorded where n is an integer of 2 to 8 in the (1,7)RLL ModulationCode, it is possible to effectively prevent the total amount of heatsupplied for forming a recording mark M from increasing excessively,whereby it is possible to prevent widening of the width of the recordingmark M and increase in cross-talk of data.

Therefore, according to this embodiment, even in the case where data areto be recorded in an optical recording medium 10 at a high linearrecording velocity, it is possible to employ a relatively inexpensivesemiconductor laser having a low output.

FIG. 7 is a block diagram showing a data recording apparatus that is apreferred embodiment of the present invention.

As shown in FIG. 7, a data recording apparatus 100 includes a spindlemotor 52 for rotating the optical recording medium 10, a head 53 forprojecting a laser beam onto the optical recording medium 10 andreceiving the light reflected by the optical recording medium 10, acontroller 54 for controlling the operation of the spindle motor 52 andthe head 53, a laser drive circuit 55 for feeding a laser drive signalto the head 53, and a lens drive circuit 56 for feeding a lens drivesignal to the optical head 53.

As shown in FIG. 7, the controller 54 includes a focus servo trackingcircuit 57, a tracking servo circuit 58 and a laser control circuit 59.

When the focus servo tracking circuit 57 is activated, a laser beam L10is focused onto the first recording layer 51 of the rotating opticalrecording medium 10 and when the tracking servo circuit 58 is activated,the spot of the laser beam L10 automatically follows the track of theoptical recording medium 10.

As shown in FIG. 7, each of the focus servo tracking circuit 57 and thetracking servo circuit 58 has an auto-gain control function forautomatically adjusting the focus gain and an auto-gain control functionfor automatically adjusting the tracking gain. Further, the lasercontrol circuit 59 is adapted to generate a laser drive signal to besupplied by the laser drive circuit 55.

In this embodiment, data for identifying the above described pulse trainpatterns are recorded in the optical recording medium 10 together withdata for identifying various recording conditions, such as a linearrecording velocity necessary for recording data, as data for settingrecording conditions in the form of wobbles or pre-pits.

Therefore, the laser control circuit 59 reads data for setting recordingconditions recorded in the optical recording medium 10 prior torecording data in the optical recording medium 10, selects the desiredpulse train pattern based on the thus read data for setting recordingconditions to generate a laser drive signal and causes the laser drivecircuit 55 to output it to the head 53.

Thus, data are recorded in the optical recording medium 10 in accordancewith the desired recording strategy.

According to this embodiment, the optical recording medium 10 isrecorded with data for identifying the pulse train patterns togetherwith data for identifying various recording conditions, such as a linearrecording velocity necessary for recording data, as data for settingrecording conditions and prior to recording data in the opticalrecording medium 10, the laser control circuit 59 reads data for settingrecording conditions recorded in the optical recording medium 10,selects the desired pulse train pattern based on the thus read data forsetting recording conditions to generate a laser drive signal andcontrol the head 53 for projecting a laser beam onto the opticalrecording medium 10. Therefore, it is possible to record data inaccordance with the desired recording strategy.

WORKING EXAMPLES AND A COMPARATIVE EXAMPLE

Hereinafter, working examples and a comparative example will be set outin order to further clarify the advantages of the present invention.

Working Example 1

An optical recording medium having the same configuration as that of theoptical recording medium 1 shown in FIG. 1 was fabricated in thefollowing manner.

A polycarbonate substrate having a thickness of 1.1 mm and a diameter of120 mm was first set on a sputtering apparatus. Then, a reflective layercontaining a mixture of Ag, Pd and Cu and having a thickness of 100 nm,a second dielectric layer containing a mixture of ZnS and SiO₂ andhaving a thickness of 30 nm, a second recording layer containing Cu as aprimary component and having a thickness of 5 nm, a first recordinglayer containing Si as a primary component and having a thickness of 5nm and a first dielectric layer containing the mixture of ZnS and SiO₂and having a thickness of 25 nm were sequentially formed on thepolycarbonate substrate using the sputtering process.

The mole ratio of ZnS to SiO₂ in the mixture of ZnS and SiO₂ containedin the first dielectric layer and the second dielectric layer was 80:20.

Further, the first dielectric layer was coated using the spin coatingmethod with an acrylic ultraviolet ray curable resin to form a coatinglayer and the coating layer was irradiated with ultraviolet rays,thereby curing the acrylic ultraviolet ray curable resin to form a lighttransmission layer having a thickness of 100 μm.

The thus fabricated optical recording medium was set in an opticalrecording medium evaluation apparatus “DDU1000” (Product Name)manufactured by Pulstec Industrial Co., Ltd. Then, a blue laser beamhaving a wavelength of 405 nm was employed as the laser beam forrecording data and the laser beam was condensed onto the opticalrecording medium via the light transmission layer using an objectivelens whose numerical aperture was 0.85, and data were recorded therein.

As a record signal, a random signal including a 2T signal to an 8Tsignal in no particular order was used and the power of a laser beam wasmodulated using the first pulse train pattern including (n−1) dividedpulses irrespective of the recording signal Data were recorded by fixingthe bottom power Pb of the first pulse train pattern to 0.5 mW andvarying the recording power Pw between the first linear recordingvelocity VL, the second linear recording velocity VM and the thirdlinear recording velocity VH.

The first linear recording velocity VL was set to 5.3 m/sec (channelclock: 66 MHz), the second linear recording velocity VM was set to 10.6m/sec (channel clock: 132-MHz) and the third linear recording velocityVH was set to 21.2 m/sec (channel clock: 263 MHz).

At the first linear recording velocity VL, when the format efficiencywas 80%, the data transfer rate was about 35 Mbps and the ratio of theshortest blank region interval to the linear recording velocity(shortest blank region interval/linear recording velocity) was 30.4nsec. Further, at the second linear recording velocity VM, when theformat efficiency was 80%, the data transfer rate was about 70 Mbps andthe ratio of the shortest blank region interval to the linear recordingvelocity (shortest blank region interval/linear recording velocity) was15.2 nsec. Moreover, at the third linear recording velocity VH, when theformat efficiency was 80%, the data transfer rate was about 140 Mbps andthe ratio of the shortest blank region interval to the linear recordingvelocity (shortest blank region interval/linear recording velocity) was7.6 nsec.

Then, data recorded in the optical recording medium were reproducedusing the above mentioned optical recording medium evaluation apparatusand the recording power Pw of the laser beam at which clock jitter ofthe reproduced signal was minimum was measured and determined as theoptical recording power. When data were to be reproduced, a laser beamhaving a wavelength of 405 nm and an objective lens having a numericalaperture NA of were employed. The fluctuation a of the reproduced signalwas measured using a time interval analyzer and the clock jitter wascalculated as aftw, where Tw was one clock period.

The results of the measurement are shown in Table 1.

Working Example 2

Data were recorded in the optical recording medium in the manner ofWorking Example 1 except that the power of the laser beam was modulatedusing the second pulse train pattern constituted so that the singlepulse pattern was selected when one of a 2T signal to a 5T signal wasrecorded and the basic pulse train pattern including two to four dividedpulses was selected when one of a 6T signal to an 8T signal wasrecorded. Then, data recorded in the optical recording medium werereproduced and the recording power Pw of the laser beam at which clockjitter of the reproduced signal was minimum was measured and determinedas the optical recording power.

The results of the measurement are shown in Table 1.

Working Example 3

Data were recorded in the optical recording medium in the manner ofWorking Example 1 except that the power of the laser beam was modulatedusing the third pulse train pattern constituted so that the single pulsepattern was selected irrespective of the recording signal. Then, datarecorded in the optical recording medium were reproduced and therecording power Pw of the laser beam at which clock jitter of thereproduced signal was minimum was measured and determined as the opticalrecording power.

The results of the measurement are shown in Table 1.

TABLE 1 Pb = 0.5 mW Second First linear linear Third linear recordingrecording recording velocity velocity velocity (VL) (VM) (VH) Firstpulse train pattern 4.5 mW 6.3 mW — Second pulse train pattern 3.5 mW4.7 mW 6.5 mW Third pulse train patter 3.1 mW 4.1 mW 5.3 mW

As shown in Table 1, it was found that in the case where the bottompower Pb was fixed at 0.5 mW, the optimum recording power became higheras the linear recording velocity increased.

Further, it was found that at each linear recording velocity, theoptical recording powers became lower in the order of the first pulsetrain pattern, the second pulse train pattern and the third pulse trainpattern.

However, since the rate of laser beam power modulation was restricted inthe optical recording medium evaluation apparatus used for theexperiments, data could not be recorded in the optical recording mediumat the third linear recording velocity VH by modulating the power of thelaser beam in accordance with the third pulse train pattern.

Working Example 4

Data were recorded in the optical recording medium in the manner ofWorking Example 1 except that the bottom power Pb of the first pulsetrain pattern was set to 1.5 mW when data were to be recorded in theoptical recording medium at the first linear recording velocity VL, thatthe bottom power Pb of the first pulse train pattern was set to 2.0 mWwhen data were to be recorded in the optical recording medium at thesecond linear recording velocity VM and that the bottom power Pb of thefirst pulse train pattern was set to 2.5 mW when data were to berecorded in the optical recording medium at the third linear recordingvelocity VH. Then, data recorded in the optical recording medium werereproduced and the recording power Pw of the laser beam at which clockjitter of the reproduced signal was minimum was measured and determinedas the optical recording power.

The results of the measurement are shown in Table 2.

In Table 2, each value in parentheses indicates the difference betweenthe optical recording power obtained in this Working Example and thatobtained in Working Example 1.

Working Example 5

Data were recorded in the optical recording medium in the manner ofWorking Example 1 except that the bottom power Pb of the second pulsetrain pattern was set to 1.5 mW when data were to be recorded in theoptical recording medium at the first linear recording velocity VL, thatthe bottom power Pb of the second pulse train pattern was set to 2.0 mWwhen data were to be recorded in the optical recording medium at thesecond linear recording velocity VM and that the bottom power Pb of thesecond pulse train pattern was set to 2.5 mW when data were to berecorded in the optical recording medium at the third linear recordingvelocity VH. Then, data recorded in the optical recording medium werereproduced and the recording power Pw of the laser beam at which clockjitter of the reproduced signal was minimum was measured and determinedas the optical recording power.

The results of the measurement are shown in Table 2.

In Table 2, each value in parentheses indicates the difference betweenthe optical recording power obtained in this Working Example and thatobtained in Working Example 2.

Working Example 6

Data were recorded in the optical recording medium in the manner ofWorking Example 1 except that the bottom power Pb of the third pulsetrain pattern was set to 1.5 mW when data were to be recorded in theoptical recording medium at the first linear recording velocity VL, thatthe bottom power Pb of the third pulse train pattern was set to 2.0 mWwhen data were to be recorded in the optical recording medium at thesecond linear recording velocity VM and that the bottom power Pb of thethird pulse train pattern was set to 2.5 mW when data were to berecorded in the optical recording medium at the third linear recordingvelocity VH. Then, data recorded in the optical recording medium werereproduced and the recording power Pw of the laser beam at which clockjitter of the reproduced signal was minimum was measured and determinedas the optical recording power.

The results of the measurement are shown in Table 2.

In Table 2, each value in parentheses indicates the difference betweenthe optical recording power obtained in this Working example and thatobtained in Working Example 3.

TABLE 2 Pb = 2.0 mW Pb = 1.5 mW Second Pb = 2.5 mW First linear linearThird linear recording recording recording velocity velocity velocity(VL) (VM) (VH) First pulse train pattern 4.2 mW (−0.3) 4.8 mW (−1.5) —Second pulse train 3.3 mW (−0.2) 3.9 mW (−0.8) 5.2 mW (−1.3) patternThird pulse train patter 3.0 mW (−0.1) 3.4 mW (−0.7) 4.3 mW (−1.0)

As shown in Table 2, it was found that in the case where the bottompower Pb of each of the pulse train patterns was set to 1.5 mW when datawere to be recorded in the optical recording medium at the first linearrecording velocity VL, the bottom power Pb of each of the pulse trainpatterns was set to 2.0 mW when data were to be recorded in the opticalrecording medium at the second linear recording velocity VM and that thebottom power Pb of each of the pulse train patterns was set to 2.5 mWwhen data were to be recorded in the optical recording medium at thethird linear recording velocity VH, the optimum recording power Pwdecreased in comparison of the case of setting the bottom power Pb ofeach of the pulse train patterns to 0.5 mW.

Further, it was found that the reduction in the optimum recording powerPw became larger as the linear recording velocity increased. It isreasonable to assume that the reason for this finding is as follows.Specifically, since the influence of heat transmitted from neighboringrecording marks becomes great as the linear recording velocityincreases, the reduction in the optimum recording power Pw caused bysetting the bottom power Pb of each of the pulse train patterns to ahigh level becomes great as the linear recording velocity increases.

Working Example 7

The recording power Pw was set to the optimum recording power obtainedin Working Example 4 and a random signal including a 2T signal to an 8Tsignal in no particular order was recorded on one track of the opticalrecording medium in the manner of Working Example 4. Then, the thusrecorded signal was reproduced and clock jitter of the reproduced signalwas measured. Hereinafter, the thus measured clock jitter is referred toas “single jitter.”

Further, a random signal including a 2T signal to an 8T signal in noparticular order was recorded on three tracks adjacent to each otherunder the same recording conditions. Then, the signal recorded in thecentral track was reproduced and clock jitter of the reproduced signalwas measured. Hereinafter, the thus measured clock jitter is referred toas “cross jitter.”

Further, the difference between the single jitter and the cross jitterwas determined for each of the linear recording velocities.

The results of the determination are shown in Table 3.

Working Example 8

The recording power Pw was set to the optimum recording power obtainedin Working Example 5 and a random signal including a 2T signal to an 8Tsignal in no particular order was recorded on one track of the opticalrecording medium in the manner of Working Example 5. Then, the thusrecorded signal was reproduced and single jitter of the reproducedsignal was measured.

Further, a random signal including a 2T signal to an 8T signal in noparticular order was recorded on three tracks adjacent with each otherunder the same recording conditions. Then, the signal recorded in thecentral track was reproduced and cross jitter of a reproduced signal wasmeasured.

Further, a difference between the single jitter and the cross jitter wasdetermined for each of the linear recording velocities.

The results of the determination are shown in Table 3.

Working Example 9

The recording power Pw was set to the optimum recording power obtainedin Working Example 6 and a random signal including a 2T signal to an 8Tsignal in no particular order was recorded on one track of the opticalrecording medium in the manner of Working Example 6. Then, the thusrecorded signal was reproduced and single jitter of the reproducedsignal was measured.

Further, a random signal including a 2T signal to an 8T signal in noparticular order was recorded on three tracks adjacent with each otherunder the same recording conditions. Then, the signal recorded in thecentral track was reproduced and cross jitter of the reproduced signalwas measured.

Further, the difference between the single jitter and the cross jitterwas determined for each of the linear recording velocities.

The results of the determination are shown in Table 3.

TABLE 3 Second First linear linear Third linear recording recordingrecording velocity velocity velocity (VL) (VM (VH) First pulse trainpattern 0.5% 0.4% — Second pulse train pattern 0.7% 0.5% 0.5% Thirdpulse train patter 1.0% 0.8% 0.5%

As shown in Table 3, it was found that in the case where data wererecorded in the optical recording medium at each of the first linearrecording velocity VL and the second linear recording velocity VM, thedifference between single jitter and cross jitter became larger andcross-talk of data increased in the order of the first pulse trainpattern, the second pulse train pattern and the third pulse trainpattern. It is reasonable to assume that this was because the width ofthe recording mark became larger in the order of the first pulse trainpattern, the second pulse train pattern and the third pulse trainpattern.

Further, it was found that the increase in the difference between singlejitter and cross jitter in the order of the first pulse train pattern,the second pulse train pattern and the third pulse train pattern waslarger in the case of recording data at the first linear recordingvelocity VL than that in the case of recording data at the second linearrecording velocity VM.

On the other hand, it was found that in the case where data wererecorded at the third linear recording velocity VH, there was nosignificant difference between the difference between single jitter andcross jitter obtained when the second pulse train pattern was employedand that obtained when the third pulse train pattern was employed.

From Working Example 1 to Working Example 9, it was found that since inthe case of recording data in the optical recording medium at the firstlinear recording velocity VL crosstalk of data increased when the powerof a laser beam was modulated using the second pulse train pattern orthe third pulse train pattern, it was preferable to modulate the powerof a laser beam using the first pulse train pattern in the case ofrecording data in the optical recording medium at the first linearrecording velocity VL. It is reasonable to conclude that the reason forthis finding is as follows. Specifically, in the case of recording datain the optical recording medium at the first linear recording velocityVL, since the linear recording velocity is low, it is not basicallyrequired to increase the level of a recording power Pw. As aconsequence, if the level of the recording power Pw is increased,cross-talk of data increases.

Further, from Working Example 1 to Working Example 9, it was found thatalthough in the case of recording data in the optical recording mediumat the second linear recording velocity VM, cross-talk of data becamelarger in the order of the first pulse train pattern, the second pulsetrain pattern and the third pulse train pattern, it was more importantto reduce the level of the recording power Pw in the case of recordingdata in the optical recording medium at the second linear recordingvelocity VM and it was therefore preferable to modulate the power of thelaser beam using the second pulse train pattern.

Furthermore, from Working Example 1 to Working Example 9, it was foundthat in the case of recording data in the optical recording medium atthe third linear recording velocity VH, since it was possible to set thelevel of the recording power Pw to the lowest level when the power ofthe laser beam was modulated using the third pulse train pattern andthere was no significant difference in the level of cross-talk of databetween when the power of the laser beam was modulated using the thirdpulse train pattern and when it was modulated by the second pulse trainpattern, it was preferable to modulate the power of the laser beam usingthe third pulse train pattern in the case of recording data in theoptical recording medium at the third linear recording velocity VH.

The present invention has thus been shown and described with referenceto a specific embodiment and Working Examples. However, it should benoted that the present invention is in no way limited to the details ofthe described arrangements but changes and modifications may be madewithout departing from the scope of the appended claims.

For example, in the above described embodiment and Working Examples,although the first recording layer 31 and the second recording layer 32are formed in contact with each other, it is not absolutely necessary toform the first recording layer 31 and the second recording layer 32 incontact with each other but it is sufficient for the second recordinglayer 32 to be so located in the vicinity of the first recording layer31 as to enable formation of a mixed region including the primarycomponent element of the first recording layer 31 and the primarycomponent element of the second recording layer 32 when the region isirradiated with a laser beam. Further, one or more other layers such asa dielectric layer may be interposed between the first recording layer31 and the second recording layer 32.

Further, in the above described embodiment, although the first recordinglayer 31 contains an element selected from the group consisting of Si,Ge, Sn, Mg, In, Zn, Bi and Al as a primary component and the secondrecording layer 32 contains Cu as a primary component, it is notabsolutely necessary for the first recording layer 31 to contain anelement selected from the group consisting of Si, Ge, Sn, Mg, In, Zn, Biand Al as a primary component and for the second recording layer 32 tocontain Cu as a primary component and the first recording layer 31 maycontain an element selected from the group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer 32 maycontain Al as a primary component. Further, the first recording layer 31may contain an element selected from the group consisting of Si, Ge, Cand Al as a primary component and the second recording layer 32 maycontain Zn as a primary component. Moreover, it is sufficient for thefirst recording layer 31 and the second recording layer 32 to containdifferent elements from each other and contain an element selected fromthe group consisting of Al, Si, Ge, C, Sn, Au, Zn, Cu, B, Mg, Ti, Mn,Fe, Ga, Zr, Ag and Pt as a primary component.

Furthermore, in the above described embodiment and Working Examples,although the optical recording medium 10 includes the first recordinglayer 31 and the second recording layer 32, the optical recording mediummay include one or more recording layers containing an element selectedfrom the group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Al as aprimary component or one or more recording layers containing Al as aprimary element, in addition to the first recording layer 31 and thesecond recording layer 32.

Moreover, although the first recording layer 31 is disposed on the sideof the light transmission layer 16 and the second recording layer 32 isdisposed on the side of the substrate 11 in the above describedembodiment and working examples, it is possible to dispose the firstrecording layer 31 on the side of the substrate 11 and the secondrecording layer 32 on the side of the light transmission layer 16.

Further, in the above described embodiment and Working Examples, theoptical recording medium 10 includes the first dielectric layer 15 andthe second dielectric layer 13 and the first recording layer 31 and thesecond recording layer 32 are disposed between the first dielectriclayer 15 and the second dielectric layer 13. However, it is notabsolutely necessary for the optical recording medium 10 to include thefirst dielectric layer 15 and the second dielectric layer 13, i.e., theoptical recording medium 10 may include no dielectric layer. Further,the optical recording medium 10 may include a single dielectric layerand in such case the dielectric layer may be disposed on either the sideof the substrate 11 or the side of the light transmission layer 16 withrespect to the first recording layer 31 and the second recording layer32.

Furthermore, in Working Examples, although the first recording layer 31and the second recording layer 32 are formed so as to have the samethickness in the above described embodiment and working examples, it isnot absolutely necessary to form the first recording layer 31 and thesecond recording layer 32 so as to have the same thickness.

Moreover, in the above described embodiment and Working Examples,although the optical recording medium 10 is provided with the reflectivelayer 12, if the level of reflected light in the recording mark M formedby the mixing an element contained in the first recording layer as aprimary component and Zn contained in the second recording layer as aprimary component and the level of reflected light in regions onto whichthe laser beam was not projected greatly differ from each other, thereflective layer may be omitted.

Furthermore, in the embodiment shown in FIG. 6, although the data forsetting recording conditions are recorded in the optical recordingmedium 10 in the form of wobbles or pre-pits, data for setting recordingconditions may be recorded in the first recording layer 31 or the secondrecording layer 32.

Moreover, in the embodiment shown in FIG. 6, although the focus servotracking circuit 57, the tracking servo circuit 58 and the laser controlcircuit 59 are incorporated into the controller 54, it is not absolutelynecessary to incorporate the focus servo tracking circuit 57, thetracking servo circuit 58 and the laser control circuit 59 into thecontroller 54, and the focus servo tracking circuit 57, the trackingservo circuit 58 and the laser control circuit 59 may be providedseparately from the controller 54. Moreover, it is alternativelypossible to install software for accomplishing functions of the focusservo tracking circuit 57, the tracking servo circuit 58 and the lasercontrol circuit 59 in the controller 54.

Further, in the above described embodiment and Working Examples,although the explanation was made as to the case where data are recordedin a next-generation type optical recording medium 10 and where it isrequired to employ a semiconductor laser having a high output,application of the present invention is not limited to the case ofrecording data in a next-generation type optical recording medium butthe present invention can be widely applied to the case of recordingdata in a write-once type optical recording medium other than anext-generation type optical recording medium.

Furthermore, in the above described embodiments, a pulse train patternis selected based on the linear recording velocity, because the width ofa recording mark M tends to become wider and cross-talk of data becomeslarger as linear recording velocity decreases. However, since cross-talkof data caused by the widening of a recording mark M increases as thetrack pitch becomes narrower and the spot diameter of the laser beambecomes larger, the pulse train pattern may be selected taking intoaccount the ratio of the track pitch TP to the spot diameter D of thelaser beam (TP/D) instead of the linear recording velocity or inaddition to the linear recording velocity. In such a case, it ispossible to select the basic pulse train pattern shown in FIG. 4 whenthe ratio of the track pitch TP to the spot diameter D of the laser beam(TP/D) is relatively small, to select the single pulse pattern shown inFIG. 5 when the ratio of the track pitch TP to the spot diameter D of alaser beam (TP/D) is relatively large, and to use the basic pulse trainpattern and the single pulse pattern in combination when the ratio ofthe track pitch TP to the spot diameter D of a laser beam (TP/D) isneither small nor large. In the case where the basic pulse train patternand the single pulse pattern are used in combination, it is possible todetermine the pulse train pattern so that the number of pulses whoselevel is set to a level corresponding to the recording power Pw becomeslarge as the ratio of the track pitch TP to the spot diameter D of alaser beam (TP/D) becomes smaller and determine the pulse train patternso that the number of pulses whose level is set to a level correspondingto the recording power Pw becomes smaller as the ratio of the trackpitch TP to the spot diameter D of a laser beam (TP/D) becomes larger.

According to the present invention, it is possible to provide a methodfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity using a laser beam having a low recording power.

Further, according to the present invention, it is possible to provide amethod for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Furthermore, according to the present invention, it is possible toprovide a method for recording data in an optical recording medium whichcan record data in a write-once type optical recording medium includingtwo or more recording layers at a high linear recording velocity using alaser beam having a low recording power.

Moreover, according to the present invention, it is possible to providean apparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium at a highlinear recording velocity using a laser beam having a low recordingpower.

Further, according to the present invention, it is possible to providean apparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Furthermore, according to the present invention, it is possible toprovide an apparatus for recording data in an optical recording mediumwhich can record data in a write-once type optical recording mediumincluding two or more recording layers at a high linear recordingvelocity using a laser beam having a low recording power.

Moreover, according to the present invention, it is possible to providean optical recording medium in which data can be recorded at a highlinear recording velocity using a laser beam having a low recordingpower.

Further, according to the present invention, it is possible to providean optical recording medium in which data can be recorded at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Furthermore, according to the present invention, it is possible toprovide an optical recording medium including two or more recordinglayers in which data can be recorded at a high linear recording velocityusing a laser beam having a low recording power.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A method for recording data in an optical recording medium whereindata are recorded in a write-once type optical recording mediumincluding at least one recording layer disposed on a substrate byprojecting a laser beam whose power is modulated in accordance with apulse train pattern including at least pulses whose levels are set tolevels corresponding to a recording power and a bottom power onto the atleast one recording layer and forming a recording mark in apredetermined region of the at least one recording layer, the method forrecording data in an optical recording medium comprising: employing apulse train pattern having a smaller number of pulses whose level is setto a level corresponding to a recording power as a linear recordingvelocity becomes higher and modulating the power of the laser beamthereby to form a recording mark in the predetermined region of the atleast one recording layer, wherein the number of pulses is set to one(1) in the case where data are to be recorded at a high linear recordingvelocity equal to or higher than a first linear recording velocity,wherein in the case where data are to be recorded at an intermediatelinear recording velocity lower than the first linear recording velocityand higher than a second linear recording velocity, the number of pulsesis set to one (1) at least when a shortest recording mark is to beformed and the number of pulses is set larger as a length of a recordingmark to be formed becomes longer, and wherein in the case where data areto be recorded at a low linear recording velocity equal to or lower thanthe second linear recording velocity, the number of pulses is set suchthat a difference between the number of pulses and a numbercorresponding to a length of each recording mark is constant, and suchthat, for at least one length of a recording mark, the number of pulsesset at the low linear recording velocity is greater than the number ofpulses set at the intermediate linear recording velocity.
 2. The methodof claim 1, wherein in the case where data are to be recorded at theintermediate linear recording velocity, the number of pulses is set toone (1) at least when the shortest recording mark is to be formed, andthe number of pulses is set larger as the linear recording velocitybecomes lower.
 3. The method of claim 1, wherein the first linearrecording velocity is equal to or higher than 10 m/sec.
 4. The method ofclaim 1, wherein the bottom power is set to a higher level as the linearrecording velocity becomes higher.
 5. The method of claim 1, wherein aratio of the bottom power to the recording power is set higher as thelinear recording velocity becomes higher.
 6. The method of claim 1,wherein data are recorded in the optical recording medium by projectingthe laser beam having a wavelength equal to or shorter than 450 nmthereonto.
 7. The method of claim 1, wherein data are recorded in theoptical recording medium by employing an objective lens and the laserbeam whose numerical aperture NA and wavelength λ satisfy λ/NA≦640 nm,and projecting the laser beam onto the optical recording medium via theobjective lens.
 8. The method of claim 1, wherein the optical recordingmedium further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatat least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.
 9. A method for recording datain an optical recording medium wherein data are recorded in a write-oncetype optical recording medium including at least one recording layerdisposed on a substrate by projecting a laser beam whose power ismodulated in accordance with a pulse train pattern including at leastpulses whose levels are set to levels corresponding to a recording powerand a bottom power onto the at least one recording layer and forming arecording mark in a predetermined region of the at least one recordinglayer, the method for recording data in an optical recording mediumcomprising: employing a pulse train pattern having a larger number ofpulses whose level is set to a level corresponding to the recordingpower as a ratio of a track pitch TP of the optical recording medium toa diameter of a spot of the laser beam becomes smaller; and modulatingthe power of the laser beam thereby to form a recording mark in thepredetermined region of the at least one recording layer.
 10. Anapparatus for recording data in an optical recording medium wherein dataare recorded in a write-once type optical recording medium including atleast one recording layer disposed on a substrate by projecting a laserbeam whose power is modulated in accordance with a pulse train patternincluding at least pulses whose levels are set to levels correspondingto a recording power and a bottom power onto the at least one recordinglayer and forming a recording mark in a predetermined region of the atleast one recording layer, the apparatus for recording data in anoptical recording medium being constituted so as to employ a pulse trainpattern having a smaller number of pulses whose level is set to a levelcorresponding to a recording power as a linear recording velocitybecomes higher and modulate the power of a laser beam thereby to form arecording mark in the predetermined region of the at least one recordinglayer, wherein a ratio of the bottom power to the recording power is sethigher as the linear recording velocity becomes higher, wherein thenumber of pulses is set to one (1) in the case where data are to berecorded at a high linear recording velocity equal to or higher than afirst linear recording velocity, wherein in the case where data are tobe recorded at an intermediate linear recording velocity lower than thefirst linear recording velocity and higher than a second linearrecording velocity, the number of pulses is set to one (1) at least whena shortest recording mark is to be formed and the number of pulses isset larger as a length of a recording mark to be formed becomes longer,and wherein in the case where data are to be recorded at a low linearrecording velocity equal to or lower than the second linear recordingvelocity, the number of pulses is set such that a difference between thenumber of pulses and a number corresponding to a length of eachrecording mark is constant, and such that, for at least one length of arecording mark, the number of pulses set at the low linear recordingvelocity is greater than the number of pulses set at the intermediatelinear recording velocity.
 11. The apparatus of claim 10, wherein in thecase where data are to be recorded at the intermediate linear recordingvelocity, the number of pulses is set to one (1) at least when theshortest recording mark is to be formed and the number of pulses is setlarger as the linear recording velocity becomes lower.
 12. The apparatusof claim 10, wherein the first linear recording velocity is equal to orhigher than 10 m/sec.
 13. A write-once type optical recording mediumcomprising a substrate and at least one recording layer disposed on thesubstrate and being constituted so that data are recorded by projectinga laser beam whose power is modulated in accordance with a pulse trainpattern including at least pulses whose levels are set to levelscorresponding to a recording power and a bottom power onto the at leastone recording layer and forming a recording mark in the at least onerecording layer, the optical recording medium being recorded with datafor: setting recording conditions necessary for employing a pulse trainpattern having a smaller number of pulses whose level is set to a levelcorresponding to the recording power as a linear recording velocitybecomes higher; setting the number of pulses to one (1) in the casewhere data are to be recorded at a high linear recording velocity equalto or higher than a first linear recording velocity; in the case wheredata are to be recorded at an intermediate linear recording velocitylower than the first linear recording velocity and higher than a secondlinear recording velocity, setting the number of pulses to one (1) atleast when a shortest recording mark is to be formed, and setting thenumber of pulses larger as a length of a recording mark to be formedbecomes longer; and in the case where data are to be recorded at a lowlinear recording velocity equal to or lower than the second linearrecording velocity, setting the number of pulses such that a differencebetween the number of pulses and a number corresponding to a length ofeach recording mark is constant and such that, for at least one lengthof a recording mark, the number of pulses set at the low linearrecording velocity is greater than the number of pulses set at theintermediate linear recording velocity, thereby modulating the power ofa laser beam.
 14. The write-once type optical recording medium of claim13, which further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and which is constituted sothat at least two recording marks are formed by projecting the laserbeam thereonto, thereby mixing an element contained in the firstrecording layer as a primary component and an element contained in thesecond recording layer as a primary component.
 15. The write-once typeoptical recording medium of claim 14, wherein the second recording layeris formed so as to be in contact with the first recording layer.
 16. Thewrite-once type optical recording medium of claim 14, wherein the lighttransmission layer is formed so as to have a thickness of 10 nm to 300nm.